Rhodium-catalyzed olefin dimerization

ABSTRACT

A process is disclosed for preparing functionalized linear olefins by dimerizing terminal olefins in the presence of a cationic rhodium compound. Novel rhodium compounds useful in this process are also disclosed.

This work was supported in part by National Science Foundation Grant Number CHE-8705534. The Government may have certain rights to this invention.

This application is a division of application Ser. No. 07/580,919, filed Sept. 11, 1990.

FIELD OF THE INVENTION

This invention relates to a process for the rhodium-catalyzed linear dimerization of terminal olefins.

BACKGROUND OF THE INVENTION

The dimerization and codimerization of α-olefinic compounds in the presence of a group VIII noble metal salt is disclosed by Alderson (U.S. Pat. No. 3,013,066). The dimerization and codimerization of alkenes and alkyl acrylates in the presence of rhodium trichloride is disclosed by Alderson et al. (J. Amer. Chem Soc. 1965, 87, 5638-5645)

Nugent et al. (J. Molecular Catalysis 1985, 29, 65-76) disclose a process for the linear dimerization of alkyl acrylates using chlorobis(ethylene)rhodium(I) dimer in combination with a Lewis acid promoter and a proton source.

Singleton (U.S. Pat. No. 4,638,084) discloses a process for dimerizing a lower alkyl acrylate or a lower alkyl methacrylate to the corresponding dialkyl hexenedioates and dialkyl 2,5-dimethylhexenedioates by contact with a catalyst prepared by reacting chlorobis(ethylene)rhodium(I) dimer and silver tetrafluoroborate.

Brookhart et al. (J. Amer. Chem. Soc. 1988, 110, 8719-8720) disclose the use of a cationic rhodium catalyst containing a pentamethylcyclopentadienyl ligand in the dimerization of ethylene to butenes.

SUMMARY OF THE INVENTION

This invention provides a process for preparing functionalized linear olefins which comprises reacting a first olefin, H₂ C═CR¹ R², with a second olefin, H₂ C═CR³ R⁴, in the presence of a cationic rhodium compound, [L¹ RhL² L³ R]⁺ X⁻ ; wherein

R¹ is selected from the group consisting of H and C₁ -C₁₀ alkyl;

R² is selected from the group consisting of H, C₁ -C₁₀ alkyl, phenyl, C₇ -C₁₂ alkyl-substituted phenyl, --COOR⁵, --C(O)NR⁶ R⁷, and --C(O)H;

R³ is selected from the group consisting of H and C₁ -C₁₀ alkyl;

R⁴ is selected from the group consisting of --COOR⁸, --C(O)NR⁹ R¹⁰, and --C(O)H;

R⁵ and R⁸ are independently selected from the group consisting of C₁ -C₁₀ alkyl;

R⁶, R⁷, R⁹, and R¹⁰ are independently selected from the group consisting of H and C₁ -C₁₀ alkyl;

L¹ is an anionic pentahapto ligand;

L² and L³ are neutral 2-electron donor ligands;

R is selected from the group of H, C₁ -C₁₀ alkyl, C₆ -C₁₀ aryl, and C₇ -C₁₀ aralkyl ligands;

X⁻ is a non-coordinating anion; and

wherein two or three of L², L³ and R are optionally connected.

This invention also provides novel compounds, I and II, which are useful in the process of this invention, ##STR1## where L⁴ is an anionic pentahapto ligand;

L⁵ is a neutral 2-electron donor ligand;

R¹¹ is selected from the group of C₁ -C₁₀ alkyl;

[X¹ ]⁻ is a non-coordinating anion;

L⁶ is an anionic pentahapto ligand;

R¹² and R¹³ are independently selected from the group consisting of C₁ -C₁₀ alkyl; and

[X² ]⁻ is a non-coordinating anion.

DETAILED DESCRIPTION OF THE INVENTION

The process of this invention can be used to homodimerize or codimerize functionalized terminal olefins in a linear, tail-to-tail fashion, or to dimerize functionalized terminal olefins with terminal alkenes. The products of the process of this invention are linear, functionalized olefins in which a carbon-carbon bond has been formed between the methylene carbons of the olefin reactants. Specific examples of useful products include dialkyl hexenedioates, which are precursors to adipic acid.

In the process of this invention, a linear functionalized olefin is prepared by reacting a first terminal olefin, CH₂ ═CR¹ R², with a second terminal olefin, CH₂ ═CR³ R⁴, in the presence of a cationic rhodium compound, [L¹ RhL² L³ R]⁺ X⁻ ; wherein

R¹ is selected from the group consisting of H and C₁ -C₁₀ alkyl;

R² is selected from the group consisting of H, C₁ -C₁₀ alkyl, phenyl, C₇ -C₁₂ alkyl-substituted phenyl, --COOR⁵, --C(O)NR⁶ R⁷, and --C(O)H;

R³ is selected from the group consisting of H and C₁ -C₁₀ alkyl;

R⁴ is selected from the group consisting of --COOR⁸, --C(O)NR⁹ R¹⁰, and --C(O)H;

R⁵ and R⁸ are independently selected from the group consisting of C₁ -C₁₀ alkyl;

R⁶, R⁷, R⁹, and R¹⁰ are independently selected from the group consisting of H and C₁ -C₁₀ alkyl;

L¹ is an anionic pentahapto ligand;

L² and L³ are neutral 2-electron donor ligands;

R is selected from the group of H, C₁ -C₁₀ alkyl, C₆ -C₁₀ aryl, and C₇ -C₁₀ aralkyl ligands;

X⁻ is a non-coordinating anion; and

wherein two or three of L², L³ and R are optionally connected.

Suitable terminal olefins, H₂ C═CR¹ R², include: ethylene; terminal alkenes containing 3-12 carbon atoms, e.g., propene, 1-butene, isoprene, 1-pentene, 1-hexene, and 1-heptene; styrene; 4-methylstyrene; alkyl acrylates, where the alkyl group contains 1-10 carbon atoms, e.g., methyl acrylate and ethyl acrylate; methyl methacrylate; acrylamide; methacrylamide; N-alkyl acrylamides, where the alkyl group contains 1-10 carbon atoms, e.g., N-methylacrylamide; N-methyl methacrylamide; N,N-dialkyl acrylamides, where the alkyl groups contain 1-10 carbon atoms, e.g., N,N-dimethylacrylamide; acrolein; and methacrolein.

Suitable functionalized terminal olefins, H₂ C═CR³ R⁴, include: alkyl acrylates, where the alkyl group contains 1-10 carbon atoms, e.g., methyl acrylate and ethyl acrylate; methyl methacrylate; acrylamide; methacrylamide; N-alkyl acrylamides, where the alkyl group contains 1-10 carbon atoms, e.g., N-methylacrylamide; N-methyl methacrylamide; N,N-dialkyl acrylamides, where the alkyl groups contain 1-10 carbon atoms, e.g., N,N-dimethylacrylamide; acrolein; and methacrolein.

Preferably, H₂ C═CR¹ R² is ethylene, propylene, styrene, methyl acrylate, ethyl acrylate, acrolein, or N,N-dimethyl acrylamide. Preferably, H₂ C═CR³ R⁴ is methyl acrylate, ethyl acrylate, acrolein, or N,N-dimethyl acrylamide. More preferably, H₂ C═CR¹ R² is ethylene, styrene, methyl acrylate or ethyl acrylate and H₂ C═CR³ R⁴ is methyl acrylate or ethyl acrylate. Most preferably, H₂ C═CR¹ R² and H₂ C═CR³ R⁴ are both either methyl acrylate or ethyl acrylate.

The terminal olefins, H₂ C═CR¹ R² and H₂ C═CR³ R⁴, can be chosen to be the same or different olefins to give, respectively, homodimers or codimers. The efficiency of the production of codimers may depend on the specific olefins chosen, and thus it may be necessary to use a large excess of one of the olefins to obtain the desired codimer.

The cationic rhodium compound used in the process of this invention can be formed in one of several ways. A particularly convenient route involves reacting a precursor, L¹ RhL^(2') L^(3'), with an acid, H⁺ X⁻, where

L¹ is an anionic pentahapto ligand;

L^(2') and L^(3') are neutral, 2-electron donor ligands, or L^(2') and L^(3') are connected to form a neutral, 4-electron ligand; and

X⁻ is a non-coordinating anion.

For example, Cp*Rh(C₂ H₄)₂ reacts with HBF₄ to give ##STR2## which is useful in the process of this invention. (Cp* is pentamethylcyclopentadienyl.) Similarly, compound Ia (L⁴ is Cp*; L⁵ is P(OMe)₃ ; R¹¹ is Me; and [X¹ ]⁻ is BF₄ ⁻) can be made by reacting HBF₄ with Cp*Rh(P(OMe)₃)(CH₂ ═CHCO₂ Me). In these routes to cationic rhodium compounds, suitable acids, H⁺ X⁻, include: HBF₄ ; HPF₆ ; H₂ SO₄ ; CF₃ SO₃ H; CF₃ CO₂ H; and tetraarylboronic acids, e.g., HBPh₄ and HB(3,5-bis(trifluoromethyl)phenyl)₄.

Alternatively, L¹ RhL^(2') (R)Y, where Y is a halide and L¹, L^(2'), and R are as defined above, can be reacted with a Lewis acid in the presence of an olefin to form a cationic rhodium compound which is useful in the process of this invention. For example, Cp*Rh(P(OMe)₃)(Me)Br could be reacted with AgBF₄ in the presence of methyl acrylate to give the desired cationic rhodium compound, [Cp*Rh(P(OMe)₃)(CH₂ ═CHCO₂ Me)(Me)]⁺ BF₄ ⁻. In catalyst preparations of this type, suitable Lewis acids include: Ag⁺ X⁻, AIX"₃, BX"₃, FeX"₃, and SbX"₅, where X" is halide.

In a third general route, precursors such as [L¹ RhL^(2') L⁴ ]⁺, where L⁴ is a π-allylic ligand and L¹ and L^(2') are as defined above, can be reacted with H₂ to give cationic rhodium compounds which are useful in the process of this invention. For example, compounds of the class [Cp*Rh(MeOC(O)CH₂ CHCHCHCO₂ Me)]⁺ X⁻ III, ##STR3## can be reacted with hydrogen to give cationic rhodium compounds which are useful in the process of this invention. A particularly useful precursor of this type is [Cp*Rh(MeOC(O)CH₂ CHCHCHCO₂ Me)]⁺ [B{3,5-bis(trifluoromethyl)phenyl}₄ ]⁻ IIIa.

In all of these rhodium compounds, suitable pentahapto ligands, L¹, L⁴ and L⁶ include: cyclopentadienyl and substituted derivatives of cyclopentadienyl containing 1-5 substitutents chosen from C₁ -C₄ alkyl, trifluoromethyl, C₆ -C₁₀ aryl, COOR¹⁴ (where R¹⁴ C₁ -C₄ alkyl), and C(O)R¹⁵ (where R¹⁵ is C₁ -C₄ alkyl); indenyl; fluorenyl; and carboranyl ligands such as (7,8,9,10,11-η)undecahydro-7,8-dicarbaundecaborato(2-) and (7,8,9,10,11-η)undecahydro-7,9-dicarbaundecaborato(2-). Preferably, L¹, L⁴ and L⁶ are alkyl-substituted derivatives of cyclopentadienyl; most preferably, L¹, L⁴ and L⁶ are pentamethylcyclopentadienyl (Cp*).

Suitable neutral, 2-electron donors, L², L³, L^(2'), L^(3'), and L⁵ include: carbon monoxide; alkyl-, aryl-, or mixed alkyl,arylphosphines (e.g., trimethylphosphine, triphenylphosphine, or diethylphenylphosphine); alkyl-, aryl-, or mixed alkyl,arylphosphites (e.g., trimethylphosphite, triphenylphosphite, or dimethylphenylphosphite); olefins (e.g., ethylene, propylene, 1-hexene, 1-octene, methyl acrylate, ethyl acrylate, or dimethyl hexenedioate); nitriles (e.g., acetonitrile or benzonitrile); and the carbonyl groups of ketones (e.g., acetone) and esters (e.g., methyl acrylate). L² and L³ can be the same or different, provided that if L² is a phosphine or phosphite, then L³ is not a phosphine or phosphite. Similarly, L^(2') and L^(3') can be the same or different, but cannot both be phosphine or phosphite ligands. Preferred 2-electron donors include carbon monoxide, ethylene, trimethylphosphite, methylacrylate and dimethyl hexenedioate.

Alternatively, L² and L³, or L^(2') and L^(3'), may be connected to form a neutral 4-electron donor ligand which contains two 2-electron-donor sites (olefin, phosphine, phosphite, nitrile or carbonyl groups). Suitable 4-electron-donor ligands of this type include: butadiene, 1,5-pentadiene, methyl vinyl ketone and acrylonitrile. Similarly, R and L² (or L^(2')) can be connected, as in ##STR4## Other suitable connected ligand systems include those in which L^(2') and L⁴ are connected (as in compound III), and those in which R is connected to L² and L³ (as in [Cp*Rh{CH(CH₂ CH₂ C(O)OMe)(CH₂ C(O)OMe)}]⁺ X⁻ (IIa), where L⁶ is Cp*, and R¹² and R¹³ are Me).

Suitable R groups include: H; C₁ -C₁₀ alkyl (e.g., methyl, ethyl, propyl, isoproyl, and butyl); C₆ -C₁₀ aryl (e.g., phenyl, p-tolyl, and 3,5-dimethylphenyl); and C₇ -C₁₀ aralkyl (e.g., benzyl, and --CH₂ CH₂ Ph).

[X]⁻, [X¹ ]⁻, and [X² ]⁻ are anions which do not coordinate to the cationic rhodium compounds, and include BF₄ -, PF₆ -, CF₃ SO₃ -, and tetraaryl borates such as [B{3,5-bis(trifluoromethyl)phenyl}₄ ]⁻ and BPh₄ -.

The novel compounds, I and II, ##STR5## where L⁴ is an anionic pentahapto ligand;

L⁵ is a neutral 2-electron donor ligand;

R¹¹ is selected from the group of C₁ -C₁₀ alkyl;

[X¹ ]⁻ is a non-coordinating anion;

L⁶ is an anionic pentahapto ligand;

R¹² and R¹³ are independently selected from the group consisting of C₁ -C₁₀ alkyl; and

[X² ]⁻ is a non-coordinating anion

are among the preferred cationic rhodium compounds for use in this invention. Preferably R¹¹, R¹² and R¹³ are methyl or ethyl, and [X² ]⁻ is a non-coordinating anion such as BF₄ -, PF₆ -, CF₃ SO₃ -, BPh₄ -, or [B{3,5-bis(trifluoromethyl)phenyl}₄ ]⁻. BF₄ - and [B{3,5-bis(trifluoromethyl)phenyl}₄ ]⁻ are most preferred. Most preferably, L⁵ is CO or trimethylphosphite.

Other preferred cationic rhodium compounds include: ##STR6## where X⁻ is a non-coordinating anion such as BF₄ - PF₆ -, CF₃ SO₃ -, BPh₄ -, or [B{3,5-bis(trifluoromethyl)-phenyl}₄ ]⁻. BF₄ - and [B{3,5-bis(trifluoromethyl)phenyl}₄ ]⁻ are most preferred.

The cationic rhodium compound can be prepared in situ in the presence of the olefin(s) to be dimerized, or it can be prepared separately and then added to the olefin(s).

The amount of cationic rhodium compound used is not critical. Molar ratios of olefin/Rh of 2/1 to 10,000/1 have been demonstrated, and higher ratios are possible.

Suitable solvents for the process of this invention are those in which the catalyst and olefin(s) are at least partially soluble, and which are not reactive under the process conditions. Suitable solvents include halocarbons, ethers, esters, and aromatic solvents. Preferred solvents include dichloromethane and diethyl ether. Alternatively, this process may be run in the absence of solvent, depending on the olefin(s). For example, the dimerization of methyl acrylate can easily be carried out in neat acrylate.

Suitable temperatures for the process of this invention range from about -100° C. to about 150° C., depending on the specific catalyst, olefin(s) and pressure. More preferably, the temperature is between 0° C. and 100° C.; most preferably between 20° C. and 80° C.

The process of this invention is not particularly sensitive to pressure, and pressures of 0.1 atm to 1,000 atm are suitable.

The process of this invention can be conducted in the presence of inert gases such as nitrogen, argon, helium, carbon dioxide and saturated hydrocarbons such as methane. In the preferred mode, the process is conducted in the presence of hydrogen, where the partial pressure of hydrogen is from about 0.1 atm to about 10 atm. Surprisingly, high yields of dimers are obtained and less than 3% saturated products are observed even under 1 atm hydrogen.

EXAMPLES

The following examples are provided to illustrate the invention and are not to be construed as limiting the invention. All preparative manipulations were carried out using conventional Schlenk techniques. Methylene chloride was distilled from P₂ O₅ under a nitrogen atmosphere. Methyl acrylate was stored under 4 Å molecular sieves. The rhodium complexes were prepared according to published procedures.

Reaction mixtures were analyzed by ¹ H NMR spectroscopy. This method is advantageous since the fate of the rhodium species as well as the conversion of methyl acrylate into dimers can be monitored. The only dimers observed in all cases were linear, tail-to-tail dimers which included E-- and Z--CH₃ OC(O)--CH═CH--CH₂ --CH₂ --CO₂ CH₃ (from here on referred to as E-2 and Z-2) and E--CH₃ OC(O)--CH₂ --CH═CH--CH₂ CO₂ CH₃ (from here on referred to as E-3). Normally, the E-2 isomer was the major isomer. Small amounts of E-3 often appeared at the end of the reaction, probably due to isomerization of the E-2 and Z-2 isomers under the reaction conditions. The turnover number (TON) was defined as the number of moles of methyl acrylate consumed/mole of rhodium complex. The most efficient reactions were carried out under 1 atm H₂. Under these conditions very little (<3%) hydrogenation of methylacrylate occurs.

Examples 1-3 demonstrate relatively inefficient dimerization employing Cp*Rh(C₂ H₄)(P(OMe)₃) as starting material. In all these examples the reaction was followed by ¹ H NMR using NMR tubes sealed under vacuum.

EXAMPLE 1

HBF₄.Me₂ O (32 μL, 0.287 mmol) is 5 mL diethyl ether was added at -30° C. to Cp*Rh(C₂ H₄)(P(OMe)₃) (84 mg, 0.215 mmol) in 25 mL ether. The rhodium hydride salt [Cp*Rh(C₂ H₄)(P(OMe)₃)H]⁺ [BF₄ ]⁻ precipitated immediately. The mixture was cooled to -80° C. and the ether solution was removed via cannula. The solid was washed with 2 portions of 5 mL of cold diethyl ether and dried under vacuum at low temperature.

Methyl acrylate (7.2 μL, 0.08 mmol) was added to an NMR tube at liquid nitrogen temperature containing [Cp*Rh(C₂ H₄)(P(OMe)₃)H]⁺ [BF₄ ]⁻ (8 mg, 0.017 mmol) in 0.6 mL CD₂ Cl₂. The NMR tube was then sealed under vacuum. The reaction was monitored by ¹ H NMR. A new complex Cp*Rh(CH₂ CH₂ CO₂ Me)(P(OMe)₃) was obtained and slow dimerization of the methyl acrylate was observed. (50% conversion after 9 days).

EXAMPLE 2

The new complex [Cp*Rh(CH₂ CH₂ CO₂ Me)(P(OMe)₃)]⁺ BF₄ ⁻ (Ia) was prepared starting from [Cp*Rh(C₂ H₄)(P(OMe)₃)H]⁺ [BF₄ ]⁻ (140 mg, 0.293 mmol) and methyl acrylate (36 μL, 0.40 mmol) in 5 mL CH₂ Cl₂. Then methyl acrylate (250 μL, 2.78 mmol) was added at room temperature. Slow dimerization was obtained: 17% conversion after 24 h and 58% after 12 days.

NMR data for [Cp*Rh(CH₂ CH₂ CO₂ Me)(P(OMe)₃)]⁺ BF₄ ⁻ (Ia):

¹ H NMR (CD₂ Cl₂, 400 MHz, 23° C.): δ3.79 (s, CO₂ CH₃), 3.71 (d, J_(P-H) =12 Hz, P(OCH₃)₃), 2.9 (m, CH₂), 2.2 (m, CH₂), 1.67 (d, J_(P-H) =4 Hz, C₅ (CH₃)₅).

¹³ C{¹ H} NMR (CD₂ Cl₂, 100 MHz, 23° C.): δ191.0 (s, CO₂ CH₃), 101.2 (s, C₅ (CH₃)₅), 55.6 (s, CO₂ CH₃), 53.2 (d, J_(P-C) =4 Hz, P(OCH₃)₃), 39.1 (s, CH₂ CO₂ CH₃), 13.0 (t, J_(Rh-C) =J_(P-C) =18 Hz, RhCH₂), 9.3 (s, C₅ (CH₃)₅).

EXAMPLE 3

Methyl acrylate (77 μL, 0.86 mmol) was added to [Cp*Rh(C₂ H₄)(P(OMe)₃)H]⁺ [BF₄ ]⁻ (12 mg, 0.025 mmol) prepared following the method described in Example 1. After 4 days, 50% conversion to dimers was obtained.

Examples 4-13 demonstrate very efficient dimerization employing Cp*Rh(C₂ H₄)₂ as starting material. Only linear dimers were obtained.

EXAMPLE 4

HBF₄.OMe₂ (one drop) was added at -40° C. to Cp*Rh(C₂ H₄)₂ (6 mg, 0.02 mmol) in 0.5 mL of CD₂ Cl₂ in an NMR tube. After shaking, the tube was frozen at liquid nitrogen temperature. Methyl acrylate (250 μL, 2.78 mmol) was added and then the tube was sealed under vacuum at liquid nitrogen temperature. The reaction was then followed by NMR analysis at room temperature. After 45 min, 97% conversion to dimers was obtained. Dimers: E-2, 94%; Z-2, 4%; E-3, 2%.

EXAMPLE 5

HBF₄.OMe₂ (one drop) was added at -50° C. to Cp*Rh(C₂ H₄)₂ (6 mg, 0.02 mmol) in 5 mL of CH₂ Cl₂ in a 100 mL Schlenk flask. Methyl acrylate (2.5 mL, 27.8 mmol) (degassed under N₂) was added at -50° C. The mixture was then stirred at 0° C. The reaction was followed by NMR by withdrawing 50 μL of the mixture and adding it to 0.5 mL of CD₂ Cl₂. After 20 h at 0° C., 63% conversion to dimers was obtained. Dimers: E-2, 86%; Z-2, 14%. TON=876.

EXAMPLE 6

The procedure described in Example 5 was repeated, except that the mixture was kept in a water bath at room temperature. After 3.83 h, 67% conversion to dimers was obtained. Dimers: E-2, 85%; Z-2, 18%. TON=931.

In Examples 7-11 and 13, HBPh₄ ** indicates HB[3,5-bis(trifluoromethyl)phenyl]₄.

EXAMPLE 7

HBPh₄ **.(Et₂ O)₂ (29 mg, 0.029 mmol) was added to Cp*Rh(C₂ H₄)₂ (6 mg, 0.020 mmol) in 5 mL CH₂ Cl₂ at 0° C. Methyl acrylate (3 mL, 33.3 mmol) was added at 0° C. and after 5 min the Schlenk flask was kept at room temperature in a water bath. Results are presented in the following table.

    ______________________________________                                         Time (h)   % Conversion to dimers                                              ______________________________________                                         0.25       5                                                                   1          16                                                                  3          45                                                                  6          62                                                                  24         75                                                                  ______________________________________                                    

At 24 h, dimers were: E-2, 89%; Z-2, 11%. TON=1249.

EXAMPLE 8

This example shows that the presence of a solvent is not necessary.

HBPh₄ **.(Et₂ O)₂ (49 mg, 0.048 mmol) in 2 mL of diethyl ether was added at 0° C. to Cp*Rh(C₂ H₄)₂ (10 mg, 0.034 mmol) in 2 mL of diethyl ether. After stirring 7 min, the mixture was evaporated to dryness at 0° C. under vacuum. Then methyl acrylate (8 mL, 88.9 mmol) was added at 0° C. to the remaining solid. After stirring 5 min, the Schlenk flask was kept in a water bath at room temperature. 47% conversion was obtained: E-2, 88%; Z-2, 12%. TON=1229.

EXAMPLE 9

This example shows that dimerization occurs at a temperature as low as -80° C.

HBPh₄ **.(Et₂ O)₂ (38 mg, 0.037 mmol) in 0.3 mL CD₂ Cl₂ was added at 0° C. to Cp*Rh(C₂ H₄)₂ (7 mg, 0.024 mmol) in 0.5 mL CD₂ Cl₂ in an NMR tube. After cooling to -80° C., methyl acrylate (20 μL, 0.222 mmol) was added, and the tube was shaken just before its introduction into the NMR probe. Dimerization was observed at -80° C., but the reaction was very slow.

In Examples 10-13, the reactions were performed using N₂ and H₂ atmospheres.

EXAMPLE 10

HBPh₄ **.(Et₂ O)₂ (49 mg, 0.048 mmol) in 2 mL CH₂ Cl₂ was added at 0° C. to Cp*Rh(C₂ H₄)₂ (10 mg, 0.034 mmol) in 10 mL CH₂ Cl₂. After stirring 10 min, methyl acrylate (8 mL, 88.9 mmol) was added to the mixture. The Schlenk flask was then kept at room temperature in a water bath. After 4 h reaction under N₂ atmosphere, 36% conversion to dimers was obtained. At this point, the mixture was divided into two fractions: one fraction was kept under N₂ and 47% conversion was finally obtained. H₂ was bubbled through the second fraction for 1 h, and 95% conversion to dimers was finally obtained. TON=2483 (H₂ atmosphere).

EXAMPLE 11

HBPh₄ **.(Et₂ O)₂ (50 mg, 0.049 mmol) in 1.5 mL CH₂ Cl₂ was added at 0° C. to Cp*Rh(C₂ H₄)₂ (10 mg, 0.034 mmol) in 2.5 mL CH₂ Cl₂. After stirring 10 min, methyl acrylate (20 mL, 222.3 mmol) was added to the solution. The Schlenk flask was then kept at room temperature in a water bath under H₂ atmosphere. The results are reported in the following table:

    ______________________________________                                         Time (h)   % Conversion to dimers                                              ______________________________________                                         4.33       14                                                                  22.33      68                                                                  48         >99.9                                                               ______________________________________                                    

At 48 h, TON=6538.

Turnover rate=3.5 mol CH₂ ═CHCO₂ Me/mol(Rh)/min at 25° C.

Dimers: E-2, 95%; Z-2, 3%; E-3, 2%.

EXAMPLE 12

One drop of HBF₄.Me₂ O was added at -40° C. to Cp*Rh(C₂ H₄)₂ (10 mg, 0.034 mmol) in 10 mL of CH₂ Cl₂. Methyl acrylate (8 mL, 88.9 mmol) was added to the mixture, and the mixture was then heated to 40°-50° C. under an H₂ atmosphere. (The Schlenk flask was equipped with a water condenser.) The reaction was only monitored for 4 h and at that point, 69% conversion was obtained.

Turnover rate=7.5 mol CH₂ ═CHCO₂ Me/mol(Rh)/min at 40° C.

EXAMPLE 13

HBPh₄ **.(Et₂ O)₂ (50 mg, 0.049 mmol) in 3 mL CH₂ Cl₂ was added at 0° C. to Cp*Rh(C₂ H₄)₂ (10 mg, 0.034 mmol) in 3 mL CH₂ Cl₂. After stirring 10 min, methyl acrylate (20 mL, 222.3 mmol) was added to the solution. The Schlenk flask was then kept at room temperature in a water bath under H₂ atmosphere. The results are reported in the following table:

    ______________________________________                                         Time (h)   % Conversion to dimers                                              ______________________________________                                         2          12                                                                  3.25       20                                                                  4.33       27                                                                  5.33       33                                                                  7.75       47                                                                  9.75       59                                                                  11.50      67                                                                  12.92      75                                                                  14.83      84                                                                  16.75      91                                                                  18.50      95                                                                  20.33      97                                                                  ______________________________________                                    

After 11.50 h, the mixture was frozen in dry ice/acetone overnight. Just after thawing, no change was noticed in the monomer/dimer ratio and the reaction was then monitored in the same manner as before freezing. After 36 h at room temperature, >99.9% conversion was obtained, giving a TON=6538. (No data points were taken between 20.33 and 36 h.)

Turnover rate=6.6 mol CH₂ ═CHCO₂ Me/mol(Rh)/min at 25° C. (over the initial 10 h period).

Dimers: E-2, 94%; Z-2, 5%; E-3, 1%.

EXAMPLE 14

The procedure described in Example 13 was repeated, except that the mixture was heated to 60° C. under H₂ atmosphere.

After 3 h, 94% conversion was obtained. An additional 20 mL of methyl acrylate was added, and after 22 h, 99% conversion was obtained at 60° C., giving a TON=13,000.

Turnover rate=65 mol CH₂ ═CHCO₂ Me/mol(Rh)/min at 60° C. (over the initial (1 h) period).

Products: Dimers (98%): E-2, 93%; Z-2, 6%; E-3, 1%, Methyl propionate (2%).

EXAMPLE 15

This example describes the synthesis (2 methods) and the characterization of the new complexes [Cp*RhCH(CH₂ CO₂ Me)(CH₂ CH₂ CO₂ Me)]⁺ [BPh₄ **]⁻ (IIb) and {Cp*Rh(η³ -MeOC(O)CH₂ CHCHCHCO₂ Me)]⁺ [BPh₄ **]⁻ (IIIb).

Method 1: HBPh₄ **.(Et₂ O)₂ (218 mg, 0.215 mmol) in 3 mL CH₂ Cl₂ was added at 0° C. to Cp*Rh(C₂ H₄)₂ (49 mg, 0.167 mmol) in 7 mL CH₂ Cl₂. After stirring 10 min, MeOC(O)CH═CHCH₂ CH₂ CO₂ Me (200 μL) was added to the mixture. After stirring overnight at room temperature, the solution was evaporated to dryness. The residue was washed with hexane to eliminate the dimer. The two complexes (IIb) and (IIIb) were separated by successive recrystallizations in diethyl ether/hexane and isolated as orange crystals.

Method 2: HBPh₄ **.(Et₂ O)₂ (171 mg, 0.169 mmol) in 3 mL CH₂ Cl₂ was added at 0° C. to Cp*Rh(C₂ H₄)₂ (39 mg, 0.133 mmol) in 7 mL CH₂ Cl₂. After stirring 10 min, methyl acrylate (240 μL, 2.668 mmol) was added to the mixture. After stirring overnight at room temperature, the solution was evaporated to dryness. The residue was washed with hexane to eliminate excess dimer. The two complexes (IIb) and (IIIb) were separated by successive recrystallizations in diethyl ether/hexane and isolated as orange crystals.

NMR data for [Cp*RhCH(CH₂ CO₂ Me)(CH₂ CH₂ CO₂ Me)]⁺ [BPh₄ **]⁻ (IIb):

¹ H NMR (400 MHz, CD₂ Cl₂, 23° C.): δ7.72 (Ph**, 8H), 7.56 (Ph**, 4H), 3.93 (s, CO₂ CH₃), 3.84 (s, CO₂ CH₃), 3.35 (m, broad, Ha), 3.00 (dd, J_(Ha-Hb) or c=9 Hz, J_(Hb-Hc) =19 Hz, Hb or c), 2.68 (d, J_(Hb-Hc))=19 Hz, Hc or b), 2.40 (ddd, J=3, 7 and 19 Hz, Hf or g), 2.15 (ddd, J=3, 9 and 19 Hz, Hg or f), 1.68 (m, Hd or e), 1.53 (s, C₅ (CH₃)₅), 1.52 (m, He or d).

¹³ C NMR (100 MHz, CD₂ Cl₂, 23° C.): δ190.4 (s, CO₂ CH₃), 183.0 (s, CO₂ CH₃), 162.1 (q, J_(C-B) =50 Hz, C1'), 135.2 (d, J_(C-H) =157.5 Hz, C2' and C6'), 129.3 (q, ² J_(C-F) =32 Hz, C3' and C5'), 125.0 (q, J_(C-F) =273 Hz, CF₃) 117.9 (dq, J_(C-H) =163 Hz, ³ J_(C-F) =4 Hz, C4'), 94.6 (d, J_(C-Rh) =8 Hz, C₅ (CH₃)₅), 55.7 (q, J_(C-H) =150 Hz, CO₂ CH₃), 54.9 (q, J_(C-H) =150 Hz, CO₂ CH₃), 44.8 (t, J_(C-H) =130 Hz, CH₂), 38.7 (dd, J_(C-Rh) =23 Hz, J_(C-H) =140 Hz, Rh-CH), 31.6 (t, J_(C-H) =130 Hz, CH₂), 29.9 (t, J_(C-H) =130, CH₂), 8.9 (q, J_(C-H) =129 Hz, C₅ (CH₃)₅). ##STR7##

NMR data for [Cp*Rh(η³ -MeOC(O)CH₂ CHCHCHCO₂ Me)]⁺ [BPh₄ **]⁻ (IIIb):

¹ H NMR (400 MHz, CD₂ Cl₂, 23° C.): δ7.72 (Ph**, 8H), 7.56 (Ph**, 4H), 5.49 (ddd, J_(Ha-Hb) =11 Hz, J_(Hc-Hb) =8 Hz, J_(Rh-Hb) =2 Hz, Hb), 4.70 (ddd, J_(Hb-Hc) =8 Hz, J_(Hc-Hd) =7.5 Hz, J_(Hc-He) =2 Hz, Hc), 3.85 (s, CO₂ CH₃), 3.82 (s, CO₂ CH₃), 3.42 (dd, J_(Hd-Hc) =7.5 Hz, J_(Hd-He) =21 Hz, Hd), 3.11 (d, J_(Ha-Hb) =11 Hz, Ha), 2.61 (dd, J_(He-Hd) =21 Hz, J_(He-Hc) =2 Hz, He), 1.70 (s, C₅ (CH₃)₅).

¹³ C{¹ H} NMR (100 MHz, CD₂ Cl₂, 23° C.): δ186.8 (s, C5), 170.0 (s, C6), 162.1 (q, J_(C-B) =50 Hz, C1'), 135.2 (s, C2' and C6'), 129.3 (q, ² J_(C-F) =32 Hz, C3' and C5'), 125.0 (q, J_(C-F) =273 Hz, CF₃), 117.9 (q, ³ J_(C-F) =4 Hz, C4'), 102.5 (d, J_(C-Rh) =5 Hz, C2), 101.3 (d, J_(C-Rh) =7 Hz, C₅ (CH₃)₅), 71.6 (d, J_(C-Rh) =9 Hz, C3), 67.8 (d, J_(C-Rh) =10 Hz, C1), 56.5 (s, OCH₃), 52.5 (s, OCH₃), 36.5, (s, C4), 8.9 (s, C₅ (CH₃).sub. 5).

¹³ C NMR (100 MHz, CD₂ Cl₂, 23° C.): δ186.8 (s, C5), 170.0 (s, C6), 162.1 (q, J_(C-B) =50 Hz, C1'), 135.2 (d, J_(C-H) =157.5 Hz, C2' and C6'), 129.3 (q, ² J_(C-F) =32 Hz, C3' and C5'), 125.0 (q, J_(C-F) =273 Hz, CF₃), 117.9 (dq, J_(C-H) =163 Hz, ³ J_(C-F) =4 Hz, C4'), 102.5 (m, J_(C-H) =170 Hz, C2), 101.3 (d, J_(C-Rh) =7 Hz, C₅ (CH₃)₅), 71.6 (m, J_(C-H) =160 Hz, C3), 67.8 (dt, J_(C-H) =161 Hz, ¹ J_(C-Rh) =² J_(C-Hb) =10 Hz, C1), 56.5 (q, J_(C-H) =151 Hz, OCH₃), 52.5 (q, J_(C-H) =148 Hz, OCH₃), 36.5, (t, J_(C-H) =130 Hz, C4), 8.9 (q, J_(C-H) =129 Hz, C₅ (CH₃)₅). 

We claim:
 1. A compound of the formulawhere L⁴ is an anionic pentahapto ligand; L⁵ is a neutral 2-electron donor ligand; R¹¹ is selected from the group of C₁ -C₁₀ alkyl; and [X¹ ]⁻ is a non-coordinating anion.
 2. A compound according to claim 1 wherein L⁴ is pentamethylcyclopentadienyl, and L⁵ is chosen from the group consisting of CO and trimethylphosphite.
 3. A compound according to claim 2 wherein L⁵ is trimethylphosphite and R¹¹ is methyl.
 4. A compound of the formula ##STR9## where L⁶ is an anionic pentahapto ligand;R¹² and R¹³ are independently selected from the group consisting of C₁ -C₁₀ alkyl; and [X² ]⁻ is a non-coordinating anion.
 5. A compound according to claim 4 wherein L⁶ is pentamethylcyclopentadienyl, and R¹² and R¹³ are methyl. 